Color television camera



A June 9, 1953 w. L. BEHREND 2,641,642

COLOR TELVISION CAMERA Filed Dec. 29, 1951- Ei g .il il Patented June 9,1953 COLOR TELEVISION CAMERA William'L. Behrend, Princeton, N.J.,1assignor to Radio Corporation of America, a corporation of DelawareApplication December 29, 1951, Serial No. 264,020

This invention relates to the type of television cameras adapted toderive a wide band brightness signal and narrow band signalsrepresentative of the intensity variations of each ofthe primary colors.l Q

According to one feature of this invention the Vproblem of registrationof the different signals l up tube. In each group of strips, successivestrips pass light of a diiferent primary color. However,

any nonlinearity in the scanning or any varia-V tion in the phase of theline scanning interval would shift the time cfoccurrence of thedifferent color signals so as to make it diicult to properly separatethem.

Therefore, in accordance with another feature of this invention meansare provided for keying the different color signals into correspondingcolor channels, irrespective of variations in phase or lack of linearityin the scanning action of the electron beam in the color pickup tube.

This latter feature of the invention may be realized by inserting keyingstrips between at least some of said groups of color strips andernploying the signals generated as the electron beam of the colorpickup tube scans across areas of its targetin registry with said keyingstrips to gate the signals derived as the beam scans across areas inregistry with the respective color strips.

In such an arrangement the keying pulses are y passed through onechannel and all the signals are passed through another channel.Variation in scanning linearity causes corresponding variations in thefrequency of the keying pulses and the different color signals. Becausethe two channels normally have different amounts of delay, their phaseversus frequency characteristics are different, and consequently .thephase relationship between the keying pulses and the color signalsvaries. Under these conditions the color signals may be gated intoincorrect channels.

In accordance with another feature of this invention therefore meanslare provided Afor holding a constant phase relationship between thecolor signals passing through one channel and the keying pulses thathave been' passed through the other.

6 Claims. (Cl. 178-5.4)

rlhis may be done by inserting a phase shifter in one channel anda delaymeans in the other. The delay circuit makes the slope of the phasevversus'frequency characteristic of the two channels identical over theband of frequencies generated due to non-linearity of the sweep and thephase shifter brings them into phase.

The manner inwhich the above'features of the invention may be realized.will be more `clearly understood after detailed consideration of thedrawings in which;

vFigure 1 is a block diagram illustrating the one embodiment of theinvention.

Figure 2'shows a section of one form of optical strip lter that 'may beused'and in addition a simple wave form that may be generated by thecolor tube as its beam scans across areas that are in registry with thevarious strips' of the filter; and

Figure k3 is a .diagram illustrating the `phase versus frequencycharacteristic of the v keying pulse channel and the signal channel'that'isusee I the scene to be televised onto the target of a Astandardblack and white full band pickupv tube 4.

` The output of this tube is a brightness signal and is applied to asuitable transmission meansvia video amplifier '5. A delay line 'i isconnected to the output of the amplifier 5 so as to equalize Y the timesat which the brightness signal and thev color signals, that pass throughcircuits described below, may arrive at the transmission means in properphase relationship. A partially reflecting mirror 6 is mounted betweenthe-lens 2 and the brightness pickup tube so as to reect some of thelight from the scene onto the face of a color pickup tube 3.

One manner in which the color pickup tube 8 may be constructed is asfollows. A vertical color strip optical filter it having groups of red,blue and-green strip filter separated by opaque strips as shown inFigure 2 is mounted on the object side of a target I2. If the pickuptubev al is of the orthicon type, the target i2 may becomprised of amica sheet having'a mosaic of photo-emissive material deposited on thebeam side. Thus as the beam scans across the target it will successivelygenerate video signals having amplitudes corresponding to the amount oflight coming through the red, blue and green filter strips respectively.A typicalsignal is indicated by the wave form l in Figure 2. As the beamscans across the opaque strips I6 the video signal has a minimum or zeroamplitude. The pickup tube 8 isillumnated by a light I8 so that even inthe black areas of a scene some light comes through the red, blue andgreen optical iilter strips and no light goes through the opaque stripI6. The amount of light passing through the color filter strips is-indicated'by Vthe dotted line "2:9 Aof Figure 2. Therefore, theYnegative pulses 2l that are generated when the beam scans across theopaque strip I6 always are of less amplitude than at the signalsgenerated when the beam scans across the color filter strips in a blackarea of a scene.

Alternatively, the color .strip lter Vcould :be mounted outside the tubeinwhichgcase :theobfject lens would focus vthe scene on it and a relaylens would be inserted between the iilter .and `the target of the tubeso as to Vimage the filter on the target. i

The signals generated by the color pickup tube are ,passed through avideo amplifier 2li to aisignal channel 26 4and a keying channel 28. Thesignal channel .-26 is comprised of a delay circuit 3l), video amplifier32 and-a clamp `circuit 34. The

clamped signals are applied to gating :devices 3B,

33 and si?. The clamps are adjusted to' a. reference Voltage suchthatfonlyithe portionof the -signal labove the dotted line 20 lor inother :words only the rscene light is passed Vthrough -the ,gates.

The keying channel `28 -is comprised Aof la video amplier 42, a fastacting clamp lll-that serves to clamp 'the signals to the negative peaksof the keying pulses 2:1, and a white level clipping circuit 46 that 'isset to clip the signals applied to it at .the level of the dotted line2U of Figure 2. In this `way only .thetportion of the keying pulse 2|'lying between :black 4level andthe dotted line 20 vare appliedtoan'amplifier ll-S'that-is tunedto the average frequency of the keyingpulses 2| so as to accentuate these pulses `and reduce theeffects ofnoise. The outputlof vthetuned amplierfd is applied to a variable .phaselshifterfll :that serves lto Vshift the phase approximately an equalamount for a range of frequencies surrounding the average frequency ofthe pulse 2l. The 'output of the variable phase shifter -59 is passedthrough a limiter52 and tisapplied rtp a gate .36, a

9,8" delay Icircuit 56, and a -lf80 delay Y,circuit 58.

All the :pulses are delayed `by 90 by a suitable setting of the phaseshifter' so that the lgates The overall-operation of the :apparatusshown in Figure l is as follows. As noted'above, variations in scanninglinearity can produce variations in -the frequency of the keying pulse2|. Generally speaking Ythe tuned .amplifier 48 has a much larger delaythan the ls ignal channel 26, and therefore the phase versus frequencycharacteristic ofthe keying channel 23 :may-be rather steep as'indicatedbythe line 6B of Figure 3. On 4the-other hand thefsignal channel 2Gmayhave a phase versus frequency characteristic such as indicated byYthe solid line 62. The delay device `3i increases the slope of theVphase versus frequency characteristic of the signal channel I2li sothat it is substantially the same as the phase versus frequencycharacteristic of the keying channel 28 as indicated by the dotted line.The phase shifter v5i) is then adjusted sothat the pulses supplied by`the limiter 52 .arrivefat kthe gate at the same time as .the videosignals produced as -the beam Ascans the red areas. Thenetresultis thateven though there are variations in the scanning speed of the beam inthe color tube 8 and consequent changes in frequency of the keying pulse2l, the

color signals passing through the signal channel 26 and keying pulsesarrive at the gates 36, 38 and 40 at the proper intervals. The phasedelay devices 55 and 58 apply the keying pulse to the gates l38 and 40:so that the gatez3-8 is capable of passing signals when A.the -beamisiopposite'the .blue strips and the gate 40 is capable of passingYsignals When .the gate is opposite the green strips. If the signalchannel 2.5 has the larger delay, the portion 1 of the 'delay 4device 30and the variable phase shifter ,fareginterchanged .-Iniapparatus'wherethe brightness signal is derived by adding full band color signals, thescanning action of the beams in the pickup tube have 'to be preciselyregistered. In the apparatus of this invention, however, preciseregistration by the scanning action of the beam in the brightness tube 4does .not .have to .be carefully registered with ,the scanning .action'inthe color tube 8 for vthe following reason. lt soihappens 'that'the.eye is highly sensitive to detail brightness but is much less sensitiveto details in color. Therefore Aeven if Vthe signals produced withcolortube 8 are not in ,precise registry ,with 'the 'brightness signalsprovided-by the .pickup tube 4 fthe eye'w'ill .not be able `to ,noticefit.

Various types of sampling sor ,gating circuits may be employed but intheparticular arrangement shown the limiter 52 Amaybe the type .used in FMreceivers. Asis well known to those skilled inrthe art, this type oflimiter clips the sine waves yapplied -to it land vthen by .use `oftuned circuits forms another sine Wavehaving ,al-fixed peak-topeakamplitude. The `gates '3.6, '3 8 Vand 4D are biased beyond cut-.off .andthe 'amplitudeof the sine .wave 'supplied .by the 'limiter L52 isvsufficient to v,overcome :this Vcut-off hias during a desired portionof its cycle.

,What wis claimed is: l

1. `A l.color :television camera comprising the combination of .a firstA.pickup `tube ,adapted .to supply -full band brightness signals, asecond pickup tube, each .of `sa'id 'tubes jhavling means' forprojecting .a 'beam of electronsy and means `adapted to Vcause `said.beam 'to scan a raster,

means .for focusing thefimages to be televised onvto each of said tubes,.a series of Vline lters -mounted in front of said second pickup tube ina .direction perpendicular to the lines A,o'f theraster .scanned by thebeam, said .stripsbeingiadapted .to pass light of different componentc.olors,.a plu- 4rality of gates connected ;to receive the Aoutputsignal of said second pickup tube, and means Y :adapted to .opensaid:gates :in :sequence Iand in synchronism with the ,scanning ;of the beam4of .said second :pickup ftube .across said :color filter strips.

2. A .color television camera Vcomprising the combination .of a ,first.pickup tube adapted to `supply brightness lsignals and a :secondY.pickup itube, said pickup tubes lha-ving felectron :guns #foreproducing electron 'beams and apparatus for causing said beams vto scana raster, optical Yapparatus A"for "focusing a lscene to .be televisedYonto -each ofi-said pickup tubes, -ineans for-causingthe signalsgenerated b-y said second tube to succesisively represent the `intensityof the different gates capable of separating and passing said signals.

3. Apparatus for deriving signals representing brightness as Well assignals representing the colors of a scene as it is being scannedcomprising in combination a first pickup tube adapted to derive signalsrepresenting apparent brightness,

a second pickup tube adapted to derive W frequency color signals thatrepresent the different selected component colors of a scene in sequenceas each line of a raster is being scanned as Well as keying pulsesextending beyond the amplitude range of said color signals, said keyingpulses occurring between at least some of the sequential groups of colorsignals, means for imaging the scene onto the light responsive areas ofeach of said pickup tubes, a plurality of gating devices, each of saidgating devices being connected so as to receive the color signalsprovided by said second pickup tube, means for successively keying saidgating devices in response to said keying signals so that each gatingdevice is able to pass only one of said color signals.

4. In a color television camera wherein one pickup tube supplies colorsignals that successively represent the selected component color of ascene as each line of the raster is scanned, and wherein keying signalsare interspersed With said color signals, apparatus for distributingsignals representing each selected component color to a different outputchannel comprising in combination a plurality of gating devices, a irstchannel for coupling said color signals to each of said gates, a secondchannel including means for selecting said keying signals, and means forcoupling said keying signals to said gates at such relative times thateach gate is rendered capable of passing signals only When the colorsignal represents a given selected component color, a delay deviceconnected in series relationship with the channel'having the leastinherent delay, the amount of said delay being such that the total delayin each channel is equalized and the phase versus frequencycharacteristics thus have the same slope, and vaphase shifterconnectedin series relationship with the other channel.

5. A color television camera comprising the combination of a iirstpick-up tube, a second pick-up tube, having means for projecting a beamof electrons and means adapted to causev said beam to scan a raster,means for focusing the images to be televised onto each of said tubes, aseries of line filters mounted inl iront of said second pick-up tube ina direction perpendicular to the lines of the raster scanned by thebeam, said strips being adapted to pass a light of diierent componentcolors, a plurality of gates connected to receive the output signal ofsaid second pick-up tube, and means adapted to open said gates insequence and in synchronisrn With the scanning of the beam of saidsecond pick-up tube across said colorlter strips.

6. A color television camera comprising the combination of a firstpick-up tube and a sec-V ond pick-up tube, said pick-up tubes havingelectron guns for producing electron beams and apparatus for causingsaid beams to scan a raster, optical apparatus for focusing a scene tobe televised onto each of said pick-up tubes, means for causing thesignals generated by said second tube to successively represent theintensity of the dify ferent component colors as its beam scans acrossthe raster, a plurality of gating devices connected to the output ofsaid second pick-up tube so as to receive said signals, and meansV forrendering said gates capable of separating and passing said signals. l

WILLIAM L. BEHREND.

References cites in the sie of thisv patent l UNITED STATES PATENTSNumber Name Date 2,492,926 Valensi Dec. 22, 1949 2,545,325 Weimer Mar.13, 1951 2,552,070 Sziklai May 8, 1951 2,579,971 Schade Dec. 25, 1951

